RPS6KB1 (ribosomal protein S6 kinase B1) is a serine/threonine kinase that functions as a critical effector downstream of mTORC1 signaling, coordinating cell growth, proliferation, and protein synthesis in response to growth factors and nutrients. Upon mTORC1 activation, RPS6KB1 phosphorylates multiple translation initiation and elongation factors including RPS6, EIF4B, and EEF2K, thereby promoting global protein synthesis 1. RPS6KB1 also regulates translation initiation by phosphorylating PDCD4 and POLDIP3/SKAR, facilitating the pioneer round of protein synthesis 23. Beyond translation control, RPS6KB1 contributes to cell survival by phosphorylating and inhibiting the pro-apoptotic protein BAD [UniProt citations]. The kinase participates in feedback regulation of mTORC1 and mTORC2 through phosphorylation of DEPTOR, MAPKAP1/SIN1, MTOR, and RICTOR 456. Under nutrient-depleted conditions, inactive RPS6KB1 associates with the EIF3 translation complex; upon mitogenic stimulation, mTORC1-mediated phosphorylation triggers dissociation and activation 7. RPS6KB1 dysfunction has been implicated in hypertrophic cardiomyopathy pathogenesis 8, highlighting its importance in cardiac homeostasis. Additionally, RPS6KB1 mediates TNF-induced insulin resistance and regulates pyrimidine biosynthesis through CAD phosphorylation, connecting metabolic stress responses to proliferative signaling 910.